Is There Anything I Can Do About Bad ESN?

Hi everyone,

Knowingly, I recently purchased an iPhone with bad ESN off of eBay. The seller and I talked about it, and she told me I should be able to just use it as an iPod (which I was planning on doing). When I got the phone, though, it would not let me avtivate it because there wasn't a SIM card in it. I use T-Mobile, so I decided to get a T-Mobile SIM card for it to plan ahead in case I ever do want to activate it. But when I finally got the SIM card, it said "SIM card is invalid". I talked to the T-Mobile support team, and they said I had to put it on service for 7 days in order to activate it with T-Mobile. So I added the phone to my plan, but it never showed up with having service and NOTHING HAS CHANGED.

I think this is because of the bad ESN or that the phone is wired for Sprint. How can I change this? Is there anything I can do about it, anything AT ALL? I'm desperate here. All I need to do is set up the iPhone, becuase I want to just use it as an iPod... I've been through the communities in Apple and T-Mobile, plus searched the Internet. Should I flash the phone? I'm going to a T-Mobile store today to see if I can get it fixed. Please don't say it's hopeless, I've also contacted the seller, hoping she can help me, becuase I feel sort of cheated as she told me I should be able to use it as an iPod with no problem whatsoever. And now I can't even get into the phone 😟

Thank you for any help you can give.